Cardiac rhythm management devices can include implantable or other ambulatory devices, such as pacemakers, cardioverter-defibrillators, cardiac resynchronization therapy (CRT) devices, or devices that can monitor one or more physiological parameters, or provide one or a combination of pacing, defibrillation, or cardiac resynchronization therapies; or that can both monitor one or more physiological parameters and provide therapy. These devices can be configured for use with multiple physiological parameter sensors, such as including implanted or external electrodes, such as to detect or treat cardiac, respiratory, or other conditions. Information obtained using the sensors can be used to provide a diagnosis, monitor a disease state, or to indicate an initiation or adjustment of therapy, among other functions.
Early detection of physiological conditions that can indicate heart failure (“HF,” sometimes referred to as congestive heart failure, “CHF”), such as before a patient experiences cardiac decompensation associated with such heart failure, can help to indicate treatment that may prevent cardiac decompensation from occurring. For example, Hatlestad et al., in U.S. Patent Application No. 2008/0082001, entitled “PHYSIOLOGICAL RESPONSE TO POSTURE CHANGE,” refers to sensing a steady state change in a physiological signal as a result of a change in posture, and generating a response. The steady state change in the physiological signal can be used to identify a heart failure condition. The steady state physiological signal can include a heart rate signal, a blood pressure signal, a heart sound energy signal, a heart rate variability signal, or a respiration rate signal.
Accurate and efficient posture detection can help to provide important information to a clinician or a cardiac rhythm management device, such as to ensure accurate interpretation of one or more physiological parameters, or to determine a therapy. Maile et al., in U.S. Pat. No. 7,559,901, entitled DETERMINING A PATIENT'S POSTURE FROM MECHANICAL VIBRATIONS OF THE HEART, refers to determining a patient's posture by monitoring heart sounds. (See Maile et al. at the Abstract.) Patient posture information can also be received from one or more accelerometers, such as can be disposed in or on a patient body, including information about a patient tilt angle. In another example, patient posture information can be discerned from thoracic impedance information, such as by clustering the thoracic impedance information, as described by Thakur et al., in U.S. Patent Application No. 61/423,128, entitled “POSTURE DETECTION USING THORACIC IMPEDANCE.”
Some cardiovascular responses corresponding to different patient postural changes are well understood. For example, Rossberg et al., in European Journal of Applied Physiology, vol. 57, page 93 (1988), entitled “INITIAL CARDIOVASCULAR RESPONSE ON CHANGE OF POSTURE FROM SQUATTING TO STANDING,” discusses differences in cardiovascular response corresponding to a first postural change from a squatting to a standing posture, and corresponding to a second postural change from a recumbent to a standing posture. For example, Rossberg et al. detected a decrease in systolic, diastolic, and mean pressure during a first heart beat after a posture change.